PICK SEA Sprint A: async sky→sea transition via WS room:sky_confirmed — TDD

- natus_save: group_send room:sky_confirmed after confirm (carries seat_role)
- consumer: sky_confirmed handler rebroadcasts to room group
- _notify_sky_confirmed() helper mirrors _notify_pick_sky_available
- sea_partial view: renders _sea_overlay.html partial for in-page injection (403 if not sky_confirmed)
- epic:sea_partial URL registered
- _natus_overlay.html: data-user-seat-role attr; _onSkyConfirmed() fetches sea partial,
  removes natus overlay + backdrop, injects sea HTML, toggles sea-open on html root;
  room:sky_confirmed WS listener calls _onSkyConfirmed only for matching seat role
- user_seat_role added to SKY_SELECT context
- FT: PickSeaAsyncTransitionTest (3 tests, ChannelsFunctionalTest) — sea overlay,
  natus gone, sea-open class — all green

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Sonnet 4.6 <noreply@anthropic.com>

src/apps/epic/urls.py

@@ -27,4 +27,5 @@ urlpatterns = [
     path('room/<uuid:room_id>/tarot/deal', views.tarot_deal, name='tarot_deal'),
     path('room/<uuid:room_id>/natus/preview', views.natus_preview, name='natus_preview'),
     path('room/<uuid:room_id>/natus/save', views.natus_save, name='natus_save'),
+    path('room/<uuid:room_id>/sea/partial', views.sea_partial, name='sea_partial'),
 ]